1. Field of the Invention
The present invention relates to a time division multiplex (TDM) switching network unit for the connection of a plurality of pulse code modulation (PCM) lines, which implements a time-wise assignment and a spatial assignment of time channels used on PCM lines for the incoming direction of transmission to time channels used on PCM lines for the outgoing direction of transmission by virture of a cyclic input of the incoming PCM words into the storage cells of its data memory, and by correspondingly delayed random reading of the outgoing PCM words from the storage cells.
2. Description of the Prior Art
In known switching networks which are constructed from switching network units of this kind (e.g. "International Zurich Seminar", 1972, B4 (1) to B4 (5)), the switching network units which are used possess an equal number of inputs and outputs, and therefore as many PCM lines for the incoming direction of transmission are connected as PCM lines for the outgoing direction of transmission.
If the number of PCM lines to be connected to a switching network exceeds the number of inputs and outputs of such switching network units, it is either possible to construct a multi-stage switching network from switching network units of this kind, or else the switching network can be formed from a plurality of single-stage switching network units, each of which comprise as many switching units as switching network components, in which case the incoming TDM lines which are connected to the switching network units are also each connected to a corresponding input of the switching network unit of every other switching network component, and equivalent outputs of these switching units within the individual switching network components are connected to one another and to an outgoing TDM line (see "Commutation & Electronique", No. 40, January 1973, Page 14-40).
The multi-stage switching network construction requires an increase in the transit times during the connection of inputs and outputs and, if the number of stages is even, an oblique load sensitivity. Although these disadvantages do not exist in the aforementioned single-stage switching network versions, instead a multiplication of the connection possibilities leads to a quadratic increase in the required switching network units.
An increase in the number of PCM lines connected to a single TDM switching network unit, in particular when these units are to be constructed in integrated circuitry, is restricted, on the one hand, by technological aspects and, on the other hand, by the clock pulse speeds required for input and output.